Actuation system for at least one hydraulically actuatable device, in particular a vehicle brake

ABSTRACT

An actuation system for at least one hydraulically actuatable device, e.g., a vehicle brake, may include an actuation device, e.g., a brake pedal, at least one first pressure source that can be actuated using the actuation device, and a second pressure source having a pressure-generating arrangement that is moveable in two directions, and which includes an electro-mechanical drive for the pressure-generating arrangement. Each pressure source is connected via at least one hydraulic line to the hydraulically actuatable device for supplying pressurising medium. A valve device may regulate pressure of the hydraulically actuatable device. Pressurising medium can be supplied in a controlled manner in both movement directions of the pressure-generating arrangement. Provision is made for two working chambers of the second pressure source to be connected by a hydraulic line, and a valve device may be arranged in the hydraulic line.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. patent application Ser. No.15/532,731, filed Oct. 24, 2017, which is a Section 371 of InternationalApplication No. PCT/EP2015/078339, filed Dec. 2, 2015, which waspublished in the German language on Jun. 9, 2016 under InternationalPublication No. WO 2016/087506 A1, which claims priority to GermanPatent Application No. 10 2014 117 727.4, filed Dec. 2, 2014, thedisclosures of which are incorporated herein by reference.

DESCRIPTION

Actuation system for at least one hydraulically actuatable device, inparticular a vehicle brake system

PRIOR ART

DE 10 2011 080312 A1 discloses a brake actuation device that providesvarious advantages, such as structural and functional integration,elimination of a pump and the associated noises, weight reduction andhigh dynamics. In this device, an intake valve and an exhaust valve areassigned to the wheel brakes, resulting in the actuation device beingstructurally relatively complicated.

Furthermore, the applicant's DE 10 2012 002 791 already describes abrake actuation device in which, for the purpose of structuralsimplification, each valve device has an intake/exhaust switching valvethat is assigned to a wheel brake, which is particularly operated inmultiplex mode (MUX).

However, the valve complexity and thus the costs are still high in thisactuation device. In this actuation device, hydraulic fluid can beconveyed during the pre-stroke and the return stroke by means of adouble-stroke piston. The delivery volume depends on the dimensions andstroke of the piston-cylinder unit.

Object of the Invention

The object of the invention is therefore to provide an inexpensiveactuation system distinguished by greater flexibility (for example inpressure control) or improved or additional applications and structuralsimplicity.

Achieving the Object

The object of the invention may be achieved with the features as recitedin the accompanying claims.

Advantageous embodiments of the invention are contained in thesub-claims, which are referred to herein.

The invention creates an actuation system that is characterised byincreased flexibility with regard to delivery volume, and therefore hasan improved or extended application range.

Thus, with corresponding volume absorption of the braking system, e.g.as a result of brake pad clearance, a relatively large active area ofthe pressure source, in particular of the double-stroke piston, can beactive at the start of volume delivery in the pre-stroke. In the case ofhigher pressure during pre-stroke and return stroke, a smaller activearea is activated by means of a valve device, in particular a solenoidvalve. The volume conveying device can not only deliver volumes into thebrake circuits, but also return volumes, e.g. for pressure reduction,from the brake circuits into the volume conveying device bycorrespondingly switching the valve device. When pressure reduction isimminent, the double-stroke piston can be positioned for maximum volumeabsorption by means of a corresponding valve circuit. If thedouble-stroke piston is not in the optimal forward position for pressurereduction, the piston can be moved into the forward stroke end positionby means of the valve device, in particular by opening the piston valves(VF, AV2), so that it can absorb the full volume during pressurereduction or return stroke. In order to balance the pressures in thebrake circuits, pressure compensation, which is not permitted to act inthe case of brake circuit failure, can be produced by a valve deviceduring pressure build-up and pressure reduction.

The invention and its embodiments create an actuation device in a veryadvantageous manner, in which, through rapid reversal of rotationdirection and valve switching, there is no appreciable interruption ofpressure reduction and pressure build-up in the suction movement of theplunger during additional delivery. The volume conveying device (VF)formed by means of the second pressure source, in particular apiston-cylinder unit, is flexible for all requirements, e.g. pressurereduction or volume overflow from the brake circuits into the volumeconveying device, positioning the piston, parallel connection of thevolume conveying device, pressure reduction from the volume conveyingdevice into the return flow and, in particular, a stepped piston withpiston surfaces in different sizes, as a result of which a reduction inthe motor torque is made possible by the smaller piston active surfaceacting by means of a corresponding valve circuit at high pressure. Inparticular, the stepped piston can have pre- and return strokes and theworking surfaces of the piston that are tuned to the torque androtational speed of the drive motor.

Furthermore, it is advantageous to connect the volume conveying device(VF) to the return flow by means of an additional valve device.

Further embodiments of the invention or of its components and otheradvantages are shown in the drawing and in the following description ofthe figures.

DESCRIPTION OF FIGURES

They show:

FIG. 1 An embodiment of the actuation system according to the invention,using the example of a brake actuation system.

FIG. 1a A combined solenoid and non-return valve as a detail of theactuation system according to FIG. 1.

The brake actuation device shown in FIG. 1 has an actuation device, inparticular a pivotably mounted brake pedal 1 that acts via a pedaltappet 1 a and an elastic mechanism or element 1 b on a first piston 2of a first pressure source in the form of a first piston-cylinder unit3. The first piston-cylinder device 3 has an additional piston 4.Pistons 5 and 6 are arranged between pistons 2, 4 or between the base ofthe first piston-cylinder unit and piston 4. A reservoir 7 is connectedvia hydraulic lines 8, 9 to the working chambers 2 a, 4 a delimited bythe pistons 2, 4. The piston-cylinder unit shown here thus has featuresof a tandem main cylinder, which can advantageously be provided withcentral valves. The pistons or cylinders can also be arranged in a twinconfiguration, i.e. parallel to each other, if the overall length isdecisive. The movement of preferably the first piston 2 can bedetermined by way of, in particular redundant, path sensors 10 a, 10 b.In this case, the sensors can be activated by two different actuatingelements, piston 2 and pedal tappet 1 a, which are connected to thesensors via corresponding, in particular mechanical, actuating devicesor elements. By inserting an elastic device 1 b, that e.g. has at leastone suitable spring, the actuating force can be measured, aside from theadditional pedal distance measurement, by the differential movement,which is very valuable for fault detection. This is described in moredetail in the applicant's German patent application DE 10 2010 050133.6,to which reference is made here for a more detailed explanation.

The electronic control and regulating unit (ECU) usually used to analysethe sensor signals and control or regulate the functions in such systemsis not shown here.

Hydraulic connections 11, 12, in which provision is made for a pressuretransmitter DG and valve devices, lead from the working chamber of thefirst piston-cylinder unit to wheel brakes (not shown here). The valvedevices have, in particular normally open, separating valves 13, 14 aswell as one, in particular a normally open, intake/exhaust solenoidvalve 15, 16, 17, 18 for each wheel brake, which are assigned to twobrake circuits BK1, BK2 in this exemplary embodiment. Alternatively, inthe case of at least one brake circuit, provision can be made forseparate intake valves EV and exhaust valves AV, as is shown in thedrawing for the lower brake circuit. The exhaust valves AV are arrangedhere in a return line R, which leads to the unpressurised reservoir 7.Furthermore, a non-return valve RV is arranged in each bypass line tothe valve EV, as is the case with existing ABS.

The separating valves 13, 14 are used in pressure modulation and brakingforce amplification. This is basically done in the same manner as in theelectro hydraulic brake, as described in the “Bremsenhandbuch” (BrakingManual), 2nd edition, published by Vieweg.

A hydraulic connection 20 leads to a path simulator 21 from the firstworking chamber of the piston-cylinder unit 3. A throttle 22 with aparallel non-return valve and a switching valve 23, which is inparticular normally closed, are arranged in the hydraulic connection 20.

A second pressure source as a function of a volume conveying device orintensifier device 25 has a second piston-cylinder unit 26 (plunger) anda high-dynamic electromotive drive 27 with a transmission 28. Thetransmission 28 is advantageously a ball screw transmission. In thiscase, the spindle acts on a plunger piston 29, which is designed as astepped double-stroke piston (DHK) and has at least two working orpressure chambers 30 a, 30 b, which are in particular delimited bydifferently sized active surfaces of the double-stroke piston. The motoracts linearly on the plunger piston 29, enabling the function of thebraking force amplification during driver braking and the pressuremodulation of a slip control system and driver assistance systems. Therotation of the motor or spindle can be sensed by means of a rotationangle sensor 24. At least in the case of brake pressures >40 bar, it isexpedient to provide the spindle pitch with self-locking or almostself-locking gears or a locking device on the transmission so that brakecircuit failure does not occur in the event of a plunger failure and aleaky safety valve 33, 34. This is advantageous when the drive motorfails during the pressure modulation and there is simultaneously a leakysafety valve 33, 34, e.g. as a result of dirt. Without self-locking, thepressure from the corresponding brake circuit would push the pistonback, which equals a brake circuit failure.

Alternatively, an additional solenoid valve 33 a, which in this case isclosed, can be inserted downstream of the safety valves. This isimportant because, with the safety valve open, both brake circuitsinteract and the redundancy of the two brake circuits is lost. In thiscase, it is favourable to make the return spring force relatively large.This prevents the pressurising medium from a brake circuit with a leakyvalve from overflowing into the other brake circuit during an ABSbraking with different pressure levels in the brake circuits.

Brake circuit failure detection (BKA) can expediently be performed bycomparing the plunger path with the pressure or motor current using thepressure-volume characteristic curve of the brake circuits or individualwheel cylinders. In the event of brake circuit failure outside the valveblock (HCU), the leaky wheel cylinder circuit is appropriately separatedby means of the corresponding intake/exhaust valve 15-18.

Hydraulic connections 31, 32 lead from the working chambers 30 a, 30 bof the second piston-cylinder unit 26 to the hydraulic connections 11,12 or the brake circuits BK1, BK2, wherein one of the aforementionedswitching valves or safety valves 33, 34 is arranged in each connection31, 32, with which the brake circuits BK1, BK2 subjected to brakepressure by the double-stroke piston 29 can be separated. In addition tovalves 33, 34, provision can be made for an additional valve in one ofthe brake circuits. This means that a redundant valve is available inthis brake circuit in the event of a brake circuit failure, and thebraking force amplification in the other circuit remains intact.

A hydraulic connection 35 leads from the working chambers 30 a, 30 b ofthe double-stroke piston 29 to the reservoir 7. Non-return valves SV1,SV2, which are assigned to the working chambers 30 a, 30 b and close tothe reservoir, are arranged in this hydraulic connection. The hydrauliclines 31, 32 originating from the working chambers 30 a, 30 b areconnected via a connecting line 40. A normally closed switching valve VFis arranged in this connecting line 40. In addition, closing non-returnvalves Ru1, RU2 are arranged in lines 31 and 32 to the wheel brakes. Inthis case, the non-return valves Ru1, RU2 are (as viewed from thedirection of working chambers 30 a, 30 b of the second pressure sourceor piston-cylinder arrangement) arranged in the hydraulic lines 31 and32, respectively, one circuit 31 (BK1) in front and the other circuit 32(BK2) behind the opening of the connecting line 40; in other words, line40 flows between valve Ru1 and valve 33 into line 31, and betweenworking chamber 30 b and valve RU2 into line 32. Thus, during the returnstroke of the double-stroke piston, the volume can flow out of theworking chamber 30 b via the open valve VF into the hydraulic line 31and the valve 33 thereby the brake circuit BK1, which is particularlyimportant when the other brake circuit fails and the valve MV describedin detail below is closed. Outflow into the working chamber 30 a isprevented by the non-return valve Ru1. At least one of the non-returnvalves Ru1, RU2 can be combined with the switching valve VF in a valvedevice or a structural unit, as is shown in detail in FIG. 1a withrespect to Ru1. Optionally, provision can also be made for a secondconnecting line 40 b between the lines 31, 32 upstream of the valves 33,34 (as viewed from the direction of the second pressure source), intowhich an additional normally closed switching valve MV is connected, forseparating the hydraulic circuits. During volume conveying, e.g. duringpressure build-up, both brake circuits 31, 32 or BK1, BK2 are suppliedwith the valve MV open. If a brake circuit fails, the valve MV can beclosed, which means that only the intact brake circuit is supplied. Aline 35 leads from line 32 (or optionally from 31) to the reservoir 7from a branch in front of the non-return valve. An additional normallyclosed switching valve AV2 is (optionally) arranged in this. When theswitching valve AV2 is open, the second pressure source or thedouble-stroke piston can be switched to a return stroke during thebraking or ABS function, without volume being conveyed into brakecircuit BK1 or BK2 during the return stroke. This means that thepressure in the brake circuits can be reduced both in multiplex mode(MUX) and without MUX, in particular in the case of μ-step when volumeconveying is insufficient for pressure reduction with the double-strokepiston 29.

If the double-stroke piston is not in the optimal forward position forpressure reduction, the piston can be moved into the forward stroke endposition by means of the valve device, in particular by opening thepiston valves (VF, AV2), so that it can absorb the full volume duringpressure reduction or return stroke. Valves 33 and 34 are closed.

In order to balance the pressures in the brake circuits, pressurecompensation, which is not permitted to act in the case of a brakecircuit failure, can be produced by a valve device (VF and MV) duringpressure build-up and pressure reduction. In this case, valve MV isclosed when valve VF is open.

In some circumstances, it may also be advantageous to make provision forthe second piston-cylinder unit (plunger) to have two working chambersin a tandem arrangement. In the inventive solution, the piston-cylinderunit 26 serves, as it were, for the brake pressure build-up and brakepressure reduction, for the realisation of the ABS and traction control,as well as assistance functions. By means of the electromotive drive,these functions can also be improved by means of finely dosed pressurecontrol with variable pressure increase velocities and, in particular,pressure loss velocities. Both the valves and hydraulic lines must bedesigned with the lowest amount of flow resistance possible, so thatadvantageously the fastest possible pressure build-up and pressurereduction can be realised by means of the piston-cylinder system. Thisensures that the piston-cylinder system or the piston speed alonedetermines the pressure build-up and pressure reduction speed. It isadvantageous to use pressure-compensated seat valves or gate valves withlow temperature dependence and a short switching time. Operation inmultiplex and the resulting advantages are described in detail in theapplicant's German patent application DE 10 2005 055751.1, to whichreference is hereby made for a more detailed explanation.

REFERENCE LIST

1 Brake pedal

1 a Pedal tappet

1 b Elastic mechanism or element

2 Piston (DK)

2 a Working chamber or pressure chamber

2 b Working chamber or pressure chamber

3 First pressure source or piston-cylinder unit

4 Piston (SK)

5 Spring

6 Spring

7 Reservoir

8 Hydraulic line

9 Hydraulic line

10 a Path sensor

10 b Path sensor

11 Hydraulic line

12 Hydraulic line

13 Isolation valve

14 Isolation valve

15 2/2-way solenoid valve

16 2/2-way solenoid valve

17 2/2-way solenoid valve

18 2/2-way solenoid valve

20 Hydraulic line

21 Path simulator

22 Throttle

23 Switching valve

24 Path or rotary sensor

25 Intensifier device

26 First pressure source or piston-cylinder unit

27 Electromotive drive

28 Transmission

29 Double-stroke piston (DHK) or plunger piston

30 a Working chamber

30 b Working chamber

31 Hydraulic line or connection

32 Hydraulic line or connection

33 Switching valve

34 Switching valve

35 Hydraulic line

36 2/2-way solenoid valve

37 Non-return valve

38 Pressure sensor

40 Hydraulic line or connection

40 b Hydraulic line or connection

AV Exhaust valve

AV2 Switching valve

BK1 Brake circuit 1

BK2 Brake circuit 2

EV Intake valve

R Return line

RV Non-return valve

RV1 Non-return valve

RV2 Non-return valve

SV1 Non-return valve

SV2 Non-return valve

MV Switching valve

VF Switching valve

What is claimed is:
 1. An actuation system for at least onehydraulically actuatable device, comprising: an actuation device, atleast one first pressure source configured to be actuated using theactuation device and a second pressure source, including: a firstworking chamber and a second working chamber; a pressure-generatingorgan that is moveable in two directions, wherein thepressure-generating organ includes a piston, and an electro-mechanicaldrive for driving the pressure-generating organ, wherein at least onefirst pressure source is connected via at the least one first hydraulicline and the second pressure source is connected via at least a secondhydraulic line and at least a third hydraulic line to the hydraulicallyactuatable device in order to supply the at least one first pressuresource and the second pressure source with pressurising medium or topressurise them, and a valve arrangement for regulating the pressure ofthe hydraulically actuatable device, wherein pressurising medium isenabled to be supplied in a controlled manner by means of the secondpressure source in both movement directions of the pressure-generatingorgan, a fourth hydraulic line that leads at least from the secondworking chamber to a reservoir; a switching valve arranged in the fourthhydraulic line, wherein the actuation system is configured to a) movethe piston of the second pressure source in a forward position; and b)initiate a return stroke of the piston during which the switching valveis open such that pressurising medium is moved from the hydraulicallyactuatable device into the first working chamber for pressure reduction.2. The actuation system according to claim 1, wherein a switching valveis arranged in at least one of the second or third hydraulic linesconnecting the second pressure source to the actuatable device.
 3. Theactuation system according to claim 1, wherein the first pressure sourcecomprises a first working chamber with a first piston and a secondworking chamber with a second piston.
 4. The actuation system accordingto claim 3, wherein each working chamber of the first pressure source isconnected via at least one first hydraulic line to the hydraulicallyactuatable device.
 5. The actuation system according to claim 1, whereina switching valve is arranged in at least one of the hydraulic linesconnecting the first pressure source to the actuatable device.
 6. Theactuation system according to claim 1, wherein the first pressure sourceis a first piston-cylinder unit, in particular a master cylinder of avehicle brake.
 7. The actuation system according to claim 1, whereinprovision is made for a hydraulic path simulator that is operativelyconnected to a working space of the first pressure source.
 8. Theactuation system according to claim 1, comprising a first brake circuitand a second brake circuit, wherein the first brake circuit comprisesthe second hydraulic line and the second brake circuit comprises thethird hydraulic line.
 9. The actuation system according to claim 8,wherein the second brake circuit comprises separate intake valves andexhaust valves, wherein the exhaust valves are arranged in a return linewhich leads to the reservoir.
 10. The actuation system according toclaim 8, wherein the first brake circuit comprises a valve assigned to afirst wheel brake and a valve assigned to a second wheel brake.
 11. Theactuation system according to claim 1, wherein a switching valve isarranged in a connecting line that connects the second and the thirdlines.
 12. The actuation system according to claim 1, further comprisingat least one switching valve for connecting the first and second workingchambers of the second pressure source and/or for connecting the secondand third hydraulic line.
 13. A method for operating a brake actuationsystem, wherein a pressure source is allocated to at least two hydrauliccircuits via at least a first hydraulic line and at least a secondhydraulic line in order to supply the first and second hydraulic lineswith pressurising medium, the pressure source including: a first workingchamber and a second working chamber; a piston that is moveable in twodirections, and an electro-mechanical drive for driving the piston,wherein the pressure source conveys pressurising medium in two deliverydirections, wherein the actuation system further comprises: a thirdhydraulic line that leads at least from the second working chamber to areservoir; and a switching valve arranged in the third hydraulic line,wherein the method comprises: a) moving the piston of the pressuresource in a forward position; and b) after moving the piston of thepressure source in the forward position, initiating a return stroke ofthe piston during which the switching valve is open such thatpressurising medium is moved from at least one of the hydraulic circuitsinto the first working chamber for pressure reduction in the at leastone of the hydraulic circuits.